1. Field of the Invention
The present invention relates to a method for controlling a dehydrating operation of a drum type washing machine, and more particularly to a method in which a speed of a motor for driving a drum is controlled to be at an optimum during spinning for reducing both a deviation of the center of gravity of a load of laundry, and a pre-spinning time period.
2. Description of the Background Art
In general, a washing machine carries out washing, rinsing and spinning operations for the removal of dirt adhering to clothes by actions of detergent and water. The washing machines of the background art include water circulation type (pulsator type), agitating type (washing rod type), and drum type washing machines.
In a drum type washing machine, the detergent, washing water and laundry are introduced into a drum having a plurality of lifters. The washing process in the drum type washing machine includes impact caused by the lifters lifting and dropping laundry, friction between the laundry and the washing water, and the chemical reaction of the detergent as the drum slowly rotates about a horizontal shaft.
Drum type washing machines are being used more frequently in the background art due to several advantageous features. For example, the laundry suffers little or no damage, laundry is prevented from entanglement, the washing effects of pounding and rubbing can be provided, and a relatively small amount of water is used in drum type washing machines.
Referring to FIG. 1, the motor of the drum type washing machine accelerates to a target revolution speed during a spinning operation of the drum type washing machine. The motor is then driven at a constant speed for a preset time period once it reaches the target revolution speed. A gravity deviation of the laundry is sensed from a variation of the revolution speed caused by the deviation of the center of gravity in the drum to determine a starting point of a main spinning cycle. In this instance, if the deviation is within a preset range, the main spinning progresses. If the deviation is not within the preset range, the motor is stopped and the motor is re-started to bring the deviation below the preset level before starting the main spinning.
However, when controlling the motor in the aforementioned manner, the motor speed rises sharply because no particular speed control is provided during the acceleration of the motor to the target revolution. The acceleration is irregular during this period due to both the deviation of the center of gravity of the laundry in the drum and the falling of the laundry in the drum. The deviation particularly increases as the laundry gathers to one side of an inside wall of the drum. Accordingly, the pre-spinning cycle requires repeated and frequent stopping and re-starting of the motor that results in a prolonged pre-spinning time period.
A spinning control method of the background art has a long pre-spinning time period, e.g., from the start of the spinning cycle to the start of the main spinning, because of the constant speed operation of the motor for the preset time period before the main spinning for sensing deviation of the center of gravity for the determination of the start of the main spinning cycle.